General Powertrain
12%of exam
Computerized Controls
32%of exam
Ignition
12%of exam
Misfire CluesScope PatternsSpark TestsIgnition Picker
Fuel + Air
16%of exam
Emission Controls
16%of exam
CatalystEVAPEGRSecondary Air
I/M Failure
12%of exam
Quick Facts
- Exam
- L1
- Credential
- Advanced Engine Performance
- Questions
- 60 total
- Scored
- 50 scored
- Time
- 150 min
- Prereq
- A8 passed
- Experience
- 3 years
- Fee
- $124 + $34
- Reference
- CV4 pop-up
- Renewal
- 5 years
Root Cause
- Symptom
- Customer complaint
- Cause
- Failed condition
- Correction
- Verified repair
- Repeat failure
- Missed root cause
- Freeze frame
- Fault snapshot
- Baseline
- Known-good comparison
Mechanical Tests
- Compression
- Cylinder sealing
- Leakdown
- Leak location
- Vacuum
- Pumping health
- Running compression
- Breathing fault
- Balance test
- Cylinder contribution
- Backpressure
- Exhaust restriction
Domain Weights
12-32-12-16-16-12
Powertrain 12Controls 32Ignition 12Fuel/air 16Emissions 16I/M 12
STFT vs LTFT
STFT
- Fast correction
- O2 feedback
- Changes quickly
LTFT
- Learned offset
- Stored correction
- Moves slowly
Immediate vs learned
Controls Picker
- Code just set→Freeze frame(Start there)
- Intermittent fault→Snapshot data(Catch event)
- Monitor marginal→Mode $06(Test values)
- Sensor plausible→Rationality check(Compare PIDs)
- Command mismatch→Bidirectional test(Verify output)
- Network codes→CAN waveform(Bus health)
- After repair→Adaptive reset(Relearn values)
- Monitor blocked→Pending DTCs(Check first)
OBD II
- Mode $01
- Live data
- Mode $02
- Freeze frame
- Mode $03
- Stored DTCs
- Mode $04
- Clear codes
- Mode $06
- Monitor results
- Mode $09
- Vehicle info
- Pending DTC
- One-trip fault
- Permanent DTC
- Monitor-cleared only
Trim Direction
Positive adds, negative removes
Positive: lean clueNegative: rich clueIdle: vacuumLoad: supply
Monitor Logic
- Continuous
- Runs often
- Non-continuous
- Needs criteria
- Enable criteria
- Run conditions
- Readiness
- Monitor completed
- Misfire
- Crank variation
- Fuel system
- Trim control
- CCM
- Component rationality
- Catalyst
- Oxygen storage
OBD Start
Code, freeze, criteria, proof
DTC firstFreeze frameEnable criteriaVerify repair
Fuel Trim
- STFT
- Immediate correction
- LTFT
- Learned correction
- Positive trim
- Adding fuel
- Negative trim
- Removing fuel
- Idle lean
- Vacuum leak
- Load lean
- Fuel shortage
- MAF error
- Wrong airflow
- Reset adaptives
- After repair
Ignition Clues
- Primary ramp
- Coil current
- Firing kV
- Spark demand
- Burn time
- Spark duration
- Misfire
- Incomplete burn
- Carbon track
- Spark leakage
- Plug gap
- kV demand
- Coil dwell
- Charge time
MAF vs MAP
MAF
- Measures mass
- Intake mounted
- Leak sensitive
MAP
- Measures pressure
- Manifold mounted
- Load estimate
Mass vs pressure
Fuel Picker
- Lean at idle→Smoke test(Vacuum leak)
- Lean under load→Volume test(Fuel supply)
- Rich both banks→Fuel pressure(Regulation)
- One cylinder lean→Injector balance(Flow issue)
- MAF suspected→VE check(Airflow proof)
- ETC replaced→Throttle relearn(Position learn)
- GDI valve deposits→Manual cleaning(No fuel wash)
- No boost→Bypass/wastegate(Control path)
Fuel Delivery
- Pressure
- Pump force
- Volume
- Flow capacity
- Leakdown
- Residual hold
- Pulse width
- Injector on-time
- Balance test
- Injector flow
- Returnless
- Module controlled
- GDI
- Cylinder injection
- Propane test
- Fuel confirmation
Pressure vs Volume
Pressure
- Static force
- Regulator clue
- May look normal
Volume
- Flow capacity
- Load clue
- Finds restrictions
Force vs delivery
Air Induction
- MAF
- Air mass
- MAP
- Manifold pressure
- TPS
- Throttle angle
- ETC
- Electronic throttle
- Unmetered air
- Post-MAF leak
- VE
- Breathing efficiency
- Turbo
- Exhaust driven
- Supercharger
- Belt driven
Upstream vs Downstream
Upstream O2
- Fuel control
- Switches fast
- Before catalyst
Downstream O2
- Catalyst monitor
- Switches slow
- After catalyst
Control vs monitor
Emissions Systems
- Catalyst
- HC/CO/NOx cleanup
- Upstream O2
- Fuel feedback
- Downstream O2
- Catalyst check
- EGR
- NOx reduction
- EVAP
- Vapor containment
- Purge
- Vapor flow
- Vent
- Seal control
- PCV
- Crankcase ventilation
Purge vs Vent
Purge
- Manifold flow
- Can enrich idle
- Normally closed
Vent
- Fresh air
- Seals testing
- Can block fill
Flow vs seal
Gas Clues
HC fuel, CO rich, NOx heat
HC: misfireCO: richNOx: heatCO2: efficiency
Misfire vs Catalyst
Misfire
- High HC
- Roughness
- Oxygen leftover
Catalyst
- Poor storage
- P0420/P0430
- Downstream switching
Cause before converter
I/M Picker
- High HC→Misfire search(Unburned fuel)
- High CO→Rich diagnosis(Incomplete oxidation)
- High NOx→EGR/cooling(Heat control)
- Catalyst incomplete→Drive cycle(Enable criteria)
- EVAP incomplete→Fuel level(Typical blocker)
- Permanent DTC→Monitor pass(Self clears)
- New catalyst fails→Root cause(Protect replacement)
- Small EVAP leak→Section isolate(Pressure decay)
Tailpipe Gases
- HC
- Unburned fuel
- CO
- Rich combustion
- NOx
- High temperature
- CO2
- Combustion efficiency
- O2
- Excess oxygen
- Lambda
- Air-fuel ratio
- ASM
- Loaded test
- TSI
- Idle test
Common Traps
Cleared codes
Readiness resets ≠ Fault not fixed
Permanent DTCs
Scanner cannot clear ≠ Monitor must pass
Catalyst replacement
Converter is symptom ≠ Root cause remains
MAF leaks
Before MAF harmless ≠ After MAF lean
Fuel pressure
Pressure can pass ≠ Volume can fail
O2 sensors
Upstream controls fuel ≠ Downstream checks catalyst
EVAP monitor
Fuel level matters ≠ Pending codes block
Last Minute
- 1.Controls 32%; 12/16 elsewhere
- 2.A8 required before L1
- 3.Use CV4 reference early
- 4.Freeze frame before clearing
- 5.Positive trim adds fuel
- 6.Idle lean suggests vacuum
- 7.Load lean suggests supply
- 8.Mode $06 shows margins
- 9.Permanent DTC self-clears
- 10.Fix catalyst root cause
- 11.HC fuel; CO rich; NOx heat
- 12.Verify repair with readiness
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